Austenitic stainless steel

ABSTRACT

An austenitic stainless steel which is suitable for use as a filler metal in gas shielded arc welding and a gas shielded arc welding process employing said steel as a filler metal. The steel consists essentially of, in weight percent, up to 0.1 percent carbon, 7.5 - 16.0 percent manganese, up to 1.0 percent silicon, 17.5 - 26.0 percent chromium, 5.0 - 17.0 percent nickel, 0.75 4.0 percent molybdenum, 0.2 - 3.8 percent nitrogen, balance iron and incidental impurities, and is additionally limited as follows: 1. The ratio of austenitizing elements to ferritizing elements is greater than 1 in accordance with the following expression: (% Ni + 30 (%C + %N) + 0.5 (%Mn)) /(%Cr + %Mo + 1.5 (%Si)) &gt; 1 2. The manganese to nitrogen ratio is at least 42; and 3. The sum of the chromium, manganese, nickel and molybdenum content is at least 38.

United States Patent [1 1 Baybrook et al.

[ AUSTENITIC STAINLESS STEEL [75] Inventors: Howard E. Baybrook, L'eechburg;

Joseph A. Chivinsky, Sarver, both of Pa.

[73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa.

[22] Filed: Oct. 16, 1972 [21] Appl. N0.: 298,055

Related U.S. Application Data [62] Division of Ser. No. 137,957. April 27. 1971, Pat.

[52] U.S. Cl 75/128, 75/128 N, 75/128 W [51] Int. Cl. C22c 39/20 [58] Field of Search 75/128 A, 128 N [56] References Cited UNITED STATES PATENTS 2.405.666 8/1946 Norwood 75/128 A 2.481.385 9/1949 Bloom 75/128 N 3.112.195 11/1963 Souvesny.... 75/128 B 3,118,761 1/1964 Hull 75/128 A 3,152,934 10/1964 Lula 75/128 A 3,171,738 3/1965 Renshaw 75/128 A 3.20l,233 8/1965 3.235.378 2/1966 Jennings 75/128 N [451 Dec. 17, 1974 Primary Examiner-Hyland Bizot Attorney, Agent, or Firm-Vincent G. Gioia; Robert F. Dropkin [57] ABSTRACT An austenitic stainless steel which is suitable for use as a filler metal in gas shielded arc welding and a gas shielded arc welding process employing said steel as a filler metal. The steel consists essentially of, in weight percent, up to 0.1 percent carbon, 7.5 16.0 percent manganese, up to 1.0 percent silicon, 17.5 26.0 percent chromium, 5.0 17.0 percent nickel, 075 4.0 percent molybdenum, 0.2 3.8 percent nitrogen, balance iron and incidental impurities, and is additionally limited as follows:

1. The ratio of austenitizing elements to ferritizing elements is greater than 1 in accordance with the following expression:

[% Ni 30 (%C %N) 0.5 (%Mn)]/[%Cr %Mo +1.5 (%Si)] 1 2. The manganese to nitrogen ratio is at least 42; and

3. The sum of the chromium, manganese, nickel and molybdenum content is at least 38.

8 Claims, No Drawings 1 AUSTENITIC STAINLESS STEEL This is a division, of application Ser. No. 137,957, filed Apr. 27, 1971 now U.S. Pat. No. 3,716,691, issued Feb. 13, 1973.

Austenitic stainless steels exhibit a combination of ments is greater than 1 in accordance with the followhighly desirable properties that make them suitable for a wide variety of industrial applications. The most common type of austenitic stainless steel is 18-8 which contains approximately 18 percent chromium and 8 percent nickel. Another type of austenitic stainless steel is described in U.S. Pat. No. 3,171,738 which issued on Mar. 2, 1965. It is comprised of molybdenum, chromium, nickel, manganese and nitrogen. More specifically, it contains up to 0.1 percent carbon, 2 3 percent molybdenum, up to 0.5 percent silicon, 7.5 9.0 percent manganese, 17.5 22 percent chromium, 5 -7 percent nickel, 0.25 0.50 percent nitrogen, balance iron and incidental impurities. Nitrogen is incorporated within the alloy to increase its strength and austenitic stability.

The alloy described in U.S. Pat. No. 3,171,738 has good corrosion resistance and good mechanical properties but is only adequate as a welding material for heavy sections. Its nitrogen content was found to be excessive and at a level which caused porous, unsound welds. More specifically, its nitrogen is at or near its equilibrium solubility level in the molten state.

An obvious way of improving the welding characteristics of the patented alloy would be to lower its nitrogen content. Unfortunately, this would adversely affect the strength of the alloy as well as its austenitic stability. As discussed above, nitrogen improves the alloys strength and has a strong austenitizing affect.

The present invention provides an alloy which is superior in certain respects, to the alloys described in the above-referred to patent. It has good welding properties as well as good corrosion resistance and good mechanical properties. Moreover, it is substantially different from those described in the prior art, such as those disclosed in U.S. Pat. Nos. 3,235,378 and 3,311,511 which respectively issued on Feb. 15, 1966 and Mar. 28, 1967. The alloy maintains a relatively high level of nitrogen through careful balancing of its chemistry and is particularly adaptable for use as a filler metal; e.g., a welding wire, in gas shielded arc welding.

It is accordingly an object of this invention to provide an austenitic stainless steel filler metal for use in gas shielded arc welding.

It is another object of this invention to provide a weldable austenitic stainless steel.

It is a further object of this invention to provide a process for producing a substantially non-porous, sound weld by arc welding in a shielding gas atmosphere.

The alloy of the present invention is a weldable austenitic stainless steel which is particularly adaptable for use as a filler metal in gas shielded arc welding. lt consists essentially of, in weight percent, up to 0.1 percent carbon, 7.5 16.0 percent manganese, up to 1.0 percent silicon, 17.5 26.0 percent chromium, 5.0 17.0 percent nickel, 0.75 4.0 percent molybdenum, 0.2 0.38 percent nitrogen, balance iron and incidental impurities; e.g., sulphur and phosphorus, and is additionally limited as follows:

ing expression:

[%Ni 30 (%C %N) 0.5 (%Mn)]/[%Cr %Mo 2. The manganese to nitrogen ratio is at least 42; and

3'. The sum of the chromium, manganese, nickel and molybdenum content is at least 38.

Chromium, molybdenum and silicon are ferritizing elements. Chromium is added for oxidation and corrosion resistance, molybdenum is added for corrosive pitting resistance, and silicon aids in the melting of the alloy, however, silicon is generally below 0.6 and preferably below 0.4 as silicon can render the alloy too fluid and hinder welding. Since they; i.e., chromium, molybdenum and silicon are ferritizers, their effect as such must be offset by the austenitizing effect of nickel, manganese, nitrogen and carbon in accordance with the following expression:

as ferrite adversely affects the alloys impact strength, corrosion resistance and hot workability. In addition to serving as austenitizers, nickel, manganese and nitrogen contribute to the properties of the alloy. For example, nickel contributes to the alloys impact strength; i.e., it contributes by being present and by rendering the alloy austenitic, manganese increases the alloys capacity for nitrogen, and nitrogen contributes to the al.- loys strength. Carbon, another austenitizer, should be kept below 0.1 and preferably 0.05 as it can cause intergranular corrosion in the weld-heat affected zone. Preferred limits for chromium, nickel, molybdenum and nitrogen are 18.5 23.0 percent chromium, l0 16 percent nickel, 2 3 percent molybdenum and 0.22 0.33 percent nitrogen. Manganese is preferably between 8.5 and 14.0 percent. We have reason to believe that manganese is an austenitizer at levels up to 10, 1 l or even 14 percent and some doubt beyond these levels, but in any event the alloy of this invention has to be austenitic and must have a ratio of austenitizing elements to ferritizing elements greater than 1, preferably greater than 1.1, in accordance with the expression set forth hereinabove. One particular group of alloys has up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 0.6 percent silicon, 18.5-23.0 percent chromium, 10.0-16.0 percent nickel, 2.0-3.0 percent molybdenum, 0.2-0.38 percent nitrogen, balance iron. Another group has up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 1.0 percent silicon, 17.5-26.0 percent chromium, 10.0-16.0 percent nickel, 0.75-4.0 percent molybdenum, 0.22-0.33 percent nitrogen, balance iron.

The manganese to nitrogen ratio must be at least 42 (preferably 45) and the sum of the chromium, manganese, nickel and molybdenum contents must be at least 38. Manganese must be present in sufficient quantity to insure thatthe alloy can accomodate its nitrogen with out producing a porous, unsound, weld, and the sum of the manganese, chromium, nickel and molybdenum content must be at least 38 to insure that the alloy is austenitic, has sufficient strength and corrosion resistance and can accommodate its nitrogen content.

The method of the present invention comprises the steps of providing two restrained metallic parts and a filler metal (weld wire) having the composition discussed above, melting the tiller metal by arc welding and depositing the molten metal between the restrained ameter, a tabulation as to the total pore area (the area members. Melting and depositing is performed in a is determined by multiplying the number of pores by shielding atmosphere and can be performed with the 1rD /4 wherein D is the average diameter of the pores) filler metal serving as an electrode or with a nonand an observance as to whether there was pore alignconsumable electrode; e.g., a tungsten electrode. Typi- 5 ment and/or pore clustering. The resultsof the analysis cal shielding atmospheres are argon, helium, nitrogen are set forth below in Table II.

TABLE I1 Weld Analysis Maximum Weld formed Niem- Pore Total Pore r from of Diameter Area Pore Pore Filler Wire Pores (Inches) (Sq. inches) Alignment Clustering A 164 0.09 0. 1086 Yes Yes B 49 0.07 0.0520 No Yes C 17 0.07 0.0205 Yes No D 9 0.06 0.0129 No No and mixture thereof. Nitrogen gas can have the addi- 20 A study of the results of Table 11 reveals that the tional benefit of increasing the nitrogen content in the soundness of the welds increases with increasing manarea of the weld. ganese to nitrogen ratios. The weld formed from filler The following examples are illustrative of the invenwire D (Mn/N r io of 65.7) was uperior to he weld tion. They are directed to the welding of stainless steel formed from filler ire C (Mn/N ratio of 40.0) which members despite the fact that the invention is believedin n was superior to h w l f rmed from filler wire to be adaptable to the welding of a variety of metals, B ratio of which in turn was p ri r to including other alloy steels and carbon steels, as the the weld formed from iiiier Wire A ratio f welding of stainless steel probably constitutes the most More p ifi y, the results Show a Q d ld important use for the invention. More specifically, they formed rom filler i e D, a Weld just Short of adequate are directed to the welding of stainless steel members Smmdess formed from iiiier wire C, and unsound h vi g up t Q1 percent b 2 3 percent l bwelds formed from filler wires B and A (a composition denum, up to 0.5 percent sili n, 7,5 9,0 percent within the range of, hereinabove referred to, U.S. Pat. manganese, 17.5 22,0 percent h i 5 7 No. 3,171,738). The soundness of a weld increases cent nickel, 0.25 0.50 percent nitrogen, balance iron with decreasing P 9 Counts, with decreasing P d i id l impurities 1 sizes, with decreasing pore area, and when pore alignment and pore clustering are minimized. EXAMPLE 1 Y One-half inch thick annealed stainless steel plates EXAMPLE n having a composition within the range of, hereinabove Th ld b d d d f h ll of hi i referred to. 115- a were welded with 40 tion has a strength substantially equivalent to the alloy several different 0.062 inch round filler wires. The described in U.S. Pat. No. 3,171,738, when welded to composition of the plates was 0.026 percent carbon, the alloy of said patent. For example, the 0.2 percent 7.50 percen m ng n .23 per n ili n. 19-70 longitudinal yield strength and ultimate tensile strength percent chromium, 6.55 percent nickel, 2.52 percent for a one-half inch annealed plate having the composimolybdenum, 0.34 percent nitrogen and balance iron. tion of the plates welded in Example I was respectively The composition of the filler wires is given below in 65 ksi and 102 ksi whereas the 0.2 percent yield Table I along with their percent manganese to percent strength and ultimate tensile strength of a weld bead nitrogen ratios. formed from 0.062 inch round filler wire D which was TABLE 1 Filler Composition (Wt. %Mn Wire C Mn Si Cr Ni Mo N Fe %N A 0.02 8.25 0.49 19.33 5.92 2.64 0.33 Bal. 25.0 B 0.019 15.93 0.28 19.43 5.75 2.55 0.44 Bal. 36.2 C 0.027 11.23 0.40 18.93 10.24 2.56 0.28 Bal. 40.0 D 0.025 13.13 0.48 19.62 15.29 2.43 0.20 Bal. 65.7

manganese and nitrogen contents for filler wire A were taken from a ladle analysis Whereas manganese and nitrogen contents for filler wires B. C and D were taken from a wire analysis.

The plates were GMAW,gas metal are welded (spray GMAW welded to one-half inch plates of said alloy arc) at a weld speed of 12 to 17 inches per minute with from said patent was respectively ksi and 105 ksi.

a current of from 295 to 305 amps in an argon-2 perit will be apparent to those skilled in the art that the cent oxygen atmosphere. Filler metal was deposited in novel principles of the invention disclosed herein in a 60 DV (double v) bevel with a one-sixteenth inch connection with specific examples thereof will suggest land. 65 various other modifications and applications of the An analysis of the welds was made using radiographic same. It is accordingly desired that in construing the (X-ray) techniques. The analysis comprised a tabulabreadth of the appended claims they shall not be limtion f h t l n m r f p r p n in a 6-in h ited to the specific examples of the invention described bead length, an observance as to the maximum pore div h i We claim:

1. An austenitic stainless steel filler metal for use in gas shielded arc welding, consisting essentially of, in weight percent, up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 0.6 percent silicon, 18.5-23.0 percent chromium, 10.0-l6.0 percent nickel, 2.0-3.0 percent molybdenum, 0.2-0.38 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression:

wherein said manganese and nitrogen contents are balanced in accordance with the following expression:

%Mn/%N 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression:

2. An austenitic stainless steel filler metal according to claim 1 having a ratio of austenitizing elements to ferritizing elements in excess of 1.1.

3. An austenitic stainless steel filler metal according to claim 1 having a percent manganese to percent nitrogen ratio of at least 45.

4. an austenitic stainless steel filler metal for use in gas shielded arc welding, consisting essentially of, in weight percent, up to 0.05 percent carbon, 13.5-14.0 percent manganese, 18.5-23.0 percent chromium, 10.0-16.0 percent nickel, 2.0-3.0 percent molybdenum, 0.22-0.33 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of l in accordance with the following expression:

+1.5(%Si)] l wherein said manganese and nitrogen contents are balanced in accordance with the following expression:

%Mn/%N 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression:

up to 0.4 percent silicon,

5. An austenitic stainless steel consisting essentially of, in weight percent, up to 0.1 percent carbon, -140 percent manganese, up to 1.0 percent silicon, 17.5-26.0 percent chromium, 10.0-16.0 percent nickel, 0.75-4.0 percent molybdenum, 022-033 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression:

+1.5 (%Si)] 1 wherein said manganese and nitrogen contents are balanced in accordance with the following expression:

%Mn/%N 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression:

6. An austenitic stainless steel according to claim 5 having a ratio of austenitizing elements to ferritizing elements in excess of 1.1.

7. An austenitic stainless steel according to claim 5 having a percent manganese to percent nitrogen ratio of at least 45.

8. An austenitic stainless steel consisting essentially of, in weight percent, up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 1.0 percent silicon, 18.5-23.0 percent chromium, l0.0-l6.0 percent nickel, 20-30 percent molybdenum, 0.2-0.38 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression:

+1.5 (%Si)] 1 wherein said manganese and nitrogen contents are balanced in accordance with the following expression:

%Mn/%N 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression: 

1. AN AUSTENITIC STAINLESS STEEL FILLER METAL FOR USE IN GAS SHIELDED ARC WELDING, CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT, UP TO 0.1 PERCENT CARBON, 8.5-14.0 PERCENT MANGANESE, UP TO 0.6 PERCENT SILICON, 18.5-23.0 PERCENT CHROMIUM, 10.0-16.0 PERCENT NICKEL, 2.0-3.0 PERCENT MOLYBDENUM, 0.2-0.38 PERCENT NITROGEN, BLANCE IRON AND INCIDENTAL IMPURITIES; WHEREIN THE RATIO OF AUSTENITIZING ELEMENTS TO FERITIZING ELEMENTS IS IN EXCESS OF 1 IN ACCORDANCE WITH THE FOLLOWING EXPRESSION: (%NI +30 (%C + %N) + 0.5 (%MN)/(%CR + %MO + 1.5 (%SI)) $ 1 WHEREIN SAID MANGANESE AND NITROGEN CONTENTS ARE BALANCED IN ACCORDANCE WITH THE FOLLOWING EXPRESSION: %MN/%N 42 AND WHEREIN THE SUM OF SAID CHROMIUM, MANGANESE, NICKEL AND MOLYBDENUM CONTENTS ARE IN ACCORDANCE WITH THE FOLLOWING EXPRESSION: %MN + %CR + %NI + %MO
 38. 2. An austenitic stainless steel filler metal according to claim 1 having a ratio of austenitizing elements to ferritizing elements in excess of 1.1.
 3. An austenitic stainless steel filler metal according to claim 1 having a percent manganese to percent nitrogen ratio of at least
 45. 4. an austenitic stainless steel filler metal for use in gas shielded arc welding, consisting essentially of, in weight percent, up to 0.05 percent carbon, 8.5-14.0 percent manganese, up to 0.4 percent silicon, 18.5-23.0 percent chromium, 10.0-16.0 percent nickel, 2.0-3.0 percent molybdenum, 0.22-0.33 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression: (%Ni + 30 (%C + %N) + 0.5 (%Mn))/(%Cr + %Mo + 1.5 (%Si)) > 1 wherein said manganese and nitrogen contents are balanced in accordance with the following expression: %Mn/%N > or = 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression: %Mn + %Cr + %Ni + %Mo > or =
 38. 5. An austenitic stainless steel consisting essentially of, in weight percent, up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 1.0 percent silicon, 17.5-26.0 percent chromium, 10.0-16.0 percent nickel, 0.75-4.0 percent molybdenum, 022-0.33 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression: (%Ni + 30 (%C + %N) + 0.5 (%Mn))/(%Cr + %Mo + 1.5 (%Si)) > 1 wherein said manganese and nitrogen contents are balanced in accordance with the following expression: %Mn/%N > or = 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression: %Mn + %Cr + %Ni + %Mo > or =
 38. 6. An austenitic stainless steel according to claim 5 having a ratio of austenitizing elements to ferritizing elements in excess of 1.1.
 7. An austenitic stainless steel according to claim 5 having a percent manganese to percent nitrogen ratio of at least
 45. 8. An austenitic stainless steel consisting essentially of, in weight percent, up to 0.1 percent carbon, 8.5-14.0 percent manganese, up to 1.0 percent silicon, 18.5-23.0 percent chromium, 10.0-16.0 percent nickel, 2.0-3.0 percent molybdenum, 0.2-0.38 percent nitrogen, balance iron and incidental impurities; wherein the ratio of austenitizing elements to ferritizing elements is in excess of 1 in accordance with the following expression: (%Ni + 30 (%C + %N) + 0.5 (%Mn))/(%Cr + %Mo + 1.5 (%Si)) > 1 wherein said manganese and nitrogen contents are balanced in accordance with the following expression: %Mn/%N > or = 42 and wherein the sum of said chromium, manganese, nickel and molybdenum contents are in accordance with the following expression: %Mn + %Cr + %Ni + %Mo > or =
 38. 